Answers

The product is an application that works with our VoIP solution. It's called Netdesktop.

In the documentation the command to deploy is the following:

msiexec /i application.msi /quiet /norestart

Installing the application manually using this command works.

However I would like to use a user "software insallation" GPO to deploy it rather than write a logon script to detect if the application is installed then use the msiexec command as admin... etc... etc... which is always a bit complicated.